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50 Cards in this Set
- Front
- Back
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What sort of reaction do stars use to make energy?
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Nuclear Fusion
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What sort of reaction do nuclear power plants on earth use to create energy?
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Nuclear Fission
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What sort of Nuclear Fusion takes place within our sun?
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The sun fuses hydrogen nuclei (single protons) into helium nuclei, which contain two protons and two neutrons.
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Both nuclear fusion and fission release energy by doing what to the nuclei of atoms?
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Nuclear fusion and nuclear fission extract energy from atoms by creating a more tightly bound nuclei. They release energy by the binding energy of atomic nuclei.
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What is required for our sun to produce one helium nucleus?
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Four hydrogen nuclei.
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When our sun converts hydrogen nuclei into a helium nucleus, the helium nucleus contains 0.7 less mass than four hydrogen nuclei. What happens to that apparently lost mass?
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It is converted into energy. You can figure out how much energy is created by using Einstein's equation E=MC^2
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How many tons of mass does the sun convert into energy per second?
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10^38
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What causes Nuclear Fusion?
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Fusion reactions can only occur when two nuclei of atoms get very close to each other. Atomic nuclei both carry positive charges however, so they are repelled away from each other. This repulsion is called the Coulomb Barriar. To overcome the barrier the nuclei must collide violently. Violent collisions only happen when the gas is very hot in which case the nuclei move around very fast and collide violently.
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What is the proton-proton chain?
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The proton-proton chain is a series of three nuclear reactions that build a helium nucleus by adding together protons. The process is efficient at temperatures above 10,000,000 K. The sun manufactures 90% of its energy this way. The proton-proton chain takes place in relatively low mass stars.
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What is Parallax?
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Parallax is the apparent change in an object in relation to the observer. Because stars are so far away their parallaxes are expressed in very small angles, usually expressed in seconds of arc.
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What is a Parsec?
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A parsec equals the distance to an imaginary star that has a parallax os 1 second of arc. A parsec is 206,265 AU, which equals roughly 3.26 ly (ight-years)
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What is intrinsic brightness?
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How much light the star actually emits.
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What is the apparent magnitude of a star?
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The apparent magnitude measures how bright a star looks from where you are.
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What is flux?
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Flux is the energy in jules (J) per second falling on 1 square meter. A joule is about as much energy as a apple falling from a tree. One joule per second is one watt.
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What is the inverse square law for light?
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The flux is inversely proportional to the square of the distance from the source. Its brightness is reduced in proportion to the square of its distance.
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What is absolute visual magnitude ?
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Astronomers have adopted 10pc as the standard distance for stars and refer to the intrinsic brightness of the star as its absolute visual magnitude (Mv), the apparent visual magnitude of the star as it would appear 10 pc away.
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What is the H-R Diagram?
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The full name is Hertzsprung-Russel diagram. The H-R Diagram is used for plotting stars on a graph that separates the effects of temperature and surface area on stellar luminosity's and enables astronomers to sort the stars according to their diameter.
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What is a visual binary star system?
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The two stars are separately visible in the telescope. The stars must have large orbits to be separately visible.
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What is a spectroscopic binary system?
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If stars in a binary system are close together they can look like one blob of light. Only by looking at a spectrum can astronomers determine that there are two stars present and not one. The doppler shift in the spectrum would tell you there were two stars and not one.
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What are eclipsing binary systems?
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An eclipsing binary star system is when you have a large star and a small star orbiting each other. When one star moves infront of the other star, it blocks some of the light. By looking at a light curve astronomers know whether they are looking at an eclipsing star system or not.
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What is the mass-luminosity relation?
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The more massive a star is, the more luminous it is.
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What is the interstellar medium?
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Interstellar medium is low-density gas and dust between stars in space. It's this dust and gas that forms into new stars. About 1 percent of the mass is made up of microscopic dust called interstellar dust.
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What is the interstellar medium called when it is easily visible as clouds of gas and dust?
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Astronomers call such a cloud a nebula from the latin word cloud. Such nebulae give clear evidence that the interstellar medium is there.
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What are the three types of Nebulae called?
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Emission Nebula, Reflection Nebula, Dark Nebula
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What is an Emission Nebula?
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Emission Nebula are produced when a hot star excites the gas near it to produce an emission spectrum. Emission Nebula have a distinct pink color that is produced by the blending of the red, blue, and violet balmer lines. Emission Nebula are also called HII regions.
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What is a Reflection Nebula?
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Reflection Nebula are produced when starlight is scattered by a dusty nebula. The spectrum of a reflection nebula is just the reflected absorption spectrum of he starlight. Reflection Nebula look blue for the same reason our sky looks blue, blue wavelengths scatter easier because they are shorter.
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What is a Dark Nebulae?
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Dark Nebulae are dense clouds of gas and dust that obstruct the view of more distant stars.
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What are molecular clouds?
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Interstellar clouds that are dense and cool enough that hydrogen can exist as molecules rather than atoms. Stars form in these clouds when the densest part of the cloud becomes unstable and gravity causes it to contract under its influence. Most clouds are not unstable enough to create stars on their own however. A stable cloud colliding with a shock wave can be compressed and disrupted into fragments. Some of these fragments may become dense enough to collapse under their own gravity and form stars.
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What do stars form out of?
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Molecular clouds. Most molecular clouds must first collide with a shock wave before they collapse in on their own gravity forming a star.
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What is a shock wave?
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Shock waves are the astronomical equivalent to a sonic boom. Supernova explosions produce shock waves that compress the interstellar medium, and recent observations show young stars forming at the edges of such shock waves. Shock waves can also be produced by the birth of very hot stars. Even the collision of two interstellar clouds can produce a shock wave and trigger cloud formation.
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What are star clusters?
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Star clusters are stars that are held together in a stable group by their combined gravity after they are formed.
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What is an association?
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An association is a group of stars that are not gravitationally bound to one another. Stars in an association drift away from each other in a few million years.
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True or False. A collapsing cloud produces more than one star
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True. A collapsing cloud of gas does not form a single star; because of instabilities in the contracting cloud, it will fragment, producing 10 to 1000 stars.
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What is a Protostar?
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A Protostar is an object that will eventually become a star.
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How are Protostars formed?
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As an interstellar cloud collpases, atoms fall inwards with no collisions. As they pick up speed and the gas becomes denser, collisions star to happen causing the atoms to move in random motions, and temperature is a measure of the random velocities of the atoms in a gas. The inward collapse of the cold gas converts gravitational energy into high random velocities, and the temperature of the gas goes up. The initial collapse of the gas forms a dense core of gas, and, as more gas falls in, a warm Protostar develops buried deep in the dusty gas.
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What are evolutionary tracks used for on the H-R Diagram?
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Evolutionary tracks are arrows that indicate a star or protostars shift on the H-R diagram.
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What is the hydrostatic equilibrium?
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The hydrostatic equilibrium is the balance between weight and pressure inside a star. Think of stars as being layered. Each layer has to be able to support the layer above it. If the center of a star is too pressurized, it will push the other layers out. If it is too weak, then the layers will start to collapse in.
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True or False. The Hydrostatic Equilibrium is the first law of stellar structure.
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False. The Hydrostatic Equilibrium is the third law of stellar structure.
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Describe the lifetime of a main sequence star.
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Main sequence stars slowly become more and more unstable as they began to use up all their hydrogen nuclei. The newly formed helium nuclei can exert the same pressure as a hydrogen nucleus, but because the gas has few nuclei, the total pressure is less. Gravity begins to constrict the core of a star which increases the temperature and causes nuclear reactions to run faster releasing more energy. This additional energy flowing outwards forces the outer layers to expand causing the star to grow larger. As the star grows larger it becomes more luminous and eventually the expansion begins to cool the surface.
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What are white dwarf stars?
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White Dwars are the remains of medium-mass stars that fused hydrogen and helium, failed to ignite carbon, drove away their outer layers to form a planetary nebulae, and collapsed and cooled to form white dwarfs. White Dwarfs are the second most common star.
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True or False. White Dwarfs are low in density.
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False. White Dwarfs are very high in density. A teaspoonful of Sirius B material would weigh more than 11 tons.
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True or False. A White Dwarf uses nuclear fusion to generate energy.
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False. White Dwarfs have exhausted their supplies of hydrogen and helium fuel and instead converts gravitational energy into thermal energy, and its interor becomes very hot; but it cannot get hot enough to ignite carbon fusion.
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Although a tremendous amount of energy flows out of the hot interior of a white dwarf, this is not how the star supports itself. How does a White Dwarf support itself?
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The white dwarf is supported against its own gravity by the inability of its degenerate electrons to pack into a smaller volume.
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True or False. White Dwarfs are stars.
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False. White Dwarfs are not called stars. They are called compact objects. White Dwargs generate no nuclear energy, is almost totally degenerate, and, except for a think layer at its surface, contains no gas. It is not a star.
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What is the future of white dwarfs?
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Whtie Dwarfs continually put off heat, and slowly began to cool down and grow fainter. Eventually white dwarfs become cold and dark and are called black-dwarfs. Our galaxy is not old enough to contain any black dwarfs.
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What is a planetary nebulae?
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A planetary nebulae actually has nothing to do with a planet. Planetary nebulae is composed of ionized gases expelled by a dying star.
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How are planetary nebulae formed?
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The process involves two stellar winds. First, an aging giant, the star gradually blows away its outer layers in a slow breeze of low-excitation gas that is not easily visible. Once the hot interior of the star is exposed, it ejects a high-speed wind that overtakes and compresses the gas of the slow wind like a snowplow, while ultraviolet radiation from the hot remains of the central star excites the gases to glow like a giant neon sign.
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What happens to massive stars when they die?
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When massive stars die it results in a supernova explosion. Supernova explosions can result in the creation of a neutron star or a black hole.
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What are pulsars?
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Pulsars are very short consistent bursts of radio waves that are given off from a neutron star.
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What is the lighthouse model of pulsars?
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Astronomers think of pulsars not as pulsing objects, but rather as objects emitting beams. As they spin, the beams sweet around the sky; when a beam sweeps over earth, observers detect a pulse of radiation. Understanding the details of this lighthouse model is a challenge, but the implications are clear. Although a neutron star is only a few kilometers in radius, it can produce powerful beams. Also, observers tend to notice only those pulsars whose beams happen to sweep over earth.
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